In a fibre-channel, arbitrated-loop (FC-AL) storage network, an FC-AL initiator, such as a RAID storage controller, is attached to one or more host devices and to one or more switch domains. Each domain typically is contained within an enclosure and includes an FC-AL switching device, a control and management node (CMN) and a plurality of FC-AL devices, such as data storage drives.
Each storage drive may be operated at one of several speeds, such as 1 Gigabit per second, 2 Gbps or 4 Gbps. In many existing networks, the speed of the devices in a domain are set at system initialization and do not change during normal operation. Moreover, the speed setting of the domains in a network is set to the speed of the switching device, regardless of the capabilities of the FC-AL devices themselves. Consequently, the domain may not be operating at an optimal speed.
One proposed solution is described in the above referenced U.S. application Ser. No. 10/995,459, entitled APPARATUS AND METHOD TO SET THE SIGNALING RATE OF A SWITCH DOMAIN DISPOSED WITHIN AN INFORMATION STORAGE AND RETRIEVAL SYSTEM, filed Nov. 22, 2004. The CMN directs that each storage device in the domain operate at the lowest speed; all devices should respond. The CMN then directs that each storage device operate at the next speed; those devices which are capable at that speed will respond. The process continues until all of the available speeds have been tested and the CMN has a record of which devices can operate at which speeds. The speed of the domain may then be set accordingly, such as to a speed at which all devices can operate.